1. Field of the Invention
This invention relates to a microcontroller. More particularly, the invention relates to an evaluation chip for trial production and evaluation developed for program developers and system board designers.
2. Description of the Related Art
An evaluation chip is generally provided as a device for trial production and evaluation to program developers and system board designers using product chips of a microcontroller. In order to allow the evaluation chip to be used in common for a plurality of product chips (mass production chips) having mutually different functional specifications, a common evaluation chip having a functional specification that is the least common multiple of the functional specifications of the product chips has been developed. Because the common evaluation chip is so constituted as to comprehensively include the functional specifications of a plurality of product chips, a greater number of peripheral resources and memories than those of the product chip are mounted. A user program is developed by the use of such a common evaluation chip and the user program so developed is mounted to the product chip. In a microcontroller capable of executing an interrupt processing in accordance with an interrupt request from a peripheral resource, an interrupt number is assigned on the 1:1 basis to the interrupt request from the peripheral resource and an interrupt processing program corresponding to the interrupt number assigned to the interrupt request is executed in response to the interrupt request from the peripheral resource.
As a technology associated with the microcontroller, Japanese Unexamined Patent Application Publication No. Hei 5-189264 discloses a microcontroller including means for permitting an external apparatus to gain access to a functional block and means for inhibiting access by the external device to the functional block when an access inhibition signal is inputted. When the same address is assigned to a functional block 1 of a microcontroller A and to a functional block 2 of a microcontroller B in a system constituted by combining the microcontrollers A and B, too, for example, only the access by the external apparatus to the functional block 1 of the microcontroller A can be executed by inputting the access inhibition signal to the microcontroller B from the external apparatus.
In an evaluation chip of a microcontroller having an LCD controller driver function, Japanese Unexamined Patent Application Publication No. Hei 6-338551 discloses a technology that changes a capacity of a general purpose memory by a program of an emulator to secure address continuity between the general purpose memory and an LCD display memory, and changes an address of the LCD display memory in accordance with a set value of a register. Japanese Unexamined Patent Application Publication No. Hei 9-305413 discloses a microcontroller having an external input terminal for inputting a signal for switching a correspondence relation between an interrupt request and a vector address (start address of interrupt processing program). In such a microcontroller, a plurality of interrupt processing programs can be selectively executed by one interrupt request without executing rewrite of a program memory because a vector select signal from the external input terminal can switch the correspondence relation between the interrupt request and the vector address.
Incidentally, the common evaluation chip has those peripheral resources and memories which are not mounted to a certain product chip A but are mounted to another product chip B. Therefore, when a user program of the product chip A is developed by using the common evaluation chip, a program developer is likely to erroneously develop a user program using the functions of those peripheral resources and memories which are not mounted to the product chip A. When the user program erroneously developed in this way is mounted to the product chip A, the product chip A does not operate normally. To avoid this problem, it may be conceivable to provide an evaluation chip corresponding on the 1:1 basis to each product but the increase of the number of man-hour for development and the product cost will occur.
In the common evaluation chip, the number of peripheral resources mounted is greater than or equal to the number of product chips. Therefore, the number of interrupt requests from the peripheral resources is greater than the number of product chips, too. When the interrupt number is assigned on the 1:1 basis to each interrupt request from the peripheral resources in the common evaluation chip, continuity of the interrupt numbers in the product chip may be lost in some cases because the interrupt numbers assigned to the interrupt requests from the peripheral resources not mounted exist depending on the product chips. Particularly when a vector table system that designates the start address of the interrupt processing program to each interrupt number is employed, an area corresponding to the interrupt number not used in the program memory becomes a free space when a discontinuous interrupt number is assigned to the interrupt request from the peripheral resource in the product chip and the program memory is consumed in vain. It may be possible to assign interrupt numbers that are different between the common evaluation chip and the product chip to secure continuity of the interrupt numbers, a program containing an erroneous setting processing may be sometimes mounted to product chip.